Polaronic conduction and Anderson localization in reduced strontium barium niobate

Journal Article · Mon Dec 07 00:00:00 EST 2015 · Applied Physics Letters

DOI:https://doi.org/10.1063/1.4937435· OSTI ID:1468470

Dandeneau, Christopher S.  ^[1]; Yang, YiHsun ^[1]; Olmstead, Marjorie A. ^[1]; Bordia, Rajendra K. ^[2]; Ohuchi, Fumio S. ^[1]

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1. Univ. of Washington, Seattle, WA (United States)
2. Clemson Univ., Clemson, SC (United States)

Electron transport mechanisms in reduced Sr_0.5Ba_0.5Nb₂O₆ (SBN50) are investigated from ~100 to 955 K through an analysis of the electrical conductivity (σ) and the Seebeck coefficient (S) with respect to temperature (T). Notably, experimental evidence is presented that supports a scenario of Anderson localization below 600 K and carrier excitation across a mobility edge at higher temperature. As a relaxor ferroelectric, stoichiometric SBN has intrinsic disorder associated with both the distribution of Sr/Ba vacancies and the formation of polarized nanoregions. The removal of oxygen through reduction generates conduction electrons in SBN. At the lowest temperatures measured (100–155 K), the electrical conductivity exhibits a temperature dependence characteristic of variable range hopping, followed by a transition to small polaron hopping at intermediate temperatures (250–545 K). In both the variable range and small polaron hopping regimes, a semiconductor-like temperature dependence of the electrical conductivity (dσ/dT > 0) was observed. However, above 615 K, dσ/dT decreases dramatically and eventually becomes metal-like (dσ/dT < 0). Concomitantly, the Seebeck coefficient exhibits a linear dependence on lnT from 615 to 955 K with the same slope (~104 μ V/K) for both polycrystalline SBN50 and single crystalline SBN61 (both reduced), indicating a similar, constant density of states near the Fermi level for both compositions. Here, the application of Seebeck coefficient theory to this inherently disordered material reveals that the excitation of carriers across a mobility edge is likely responsible for the change in dσ/dT at high temperature. Such findings may have a significant impact in the field of conductive ferroelectrics.

• Research Organization: Univ. of Washington, Seattle, WA (United States)
• Sponsoring Organization: USDOE Office of Fossil Energy (FE)
• Grant/Contract Number: FE0007272
• OSTI ID: 1468470
• Alternate ID(s): OSTI ID: 1228437
• Journal Information: Applied Physics Letters, Vol. 107, Issue 23; ISSN 0003-6951
• Publisher: American Institute of Physics (AIP)
• Country of Publication: United States
• Language: English

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36 MATERIALS SCIENCE